Machine for treating infectious waste, in particular medical waste

ABSTRACT

A machine including a shredder formed by at least two parallel series of contrarotating knives, alternating with counter-knives; the knives are carried by shafts; the edge of each counter-knife facing the opposite knife associated thereto comprises an arcuate portion. At least one counter-knife has a portion extending above the axis of the shaft and forming an arcuate edge centered on the axis of the other shaft of the shredder, this arcuate edge completing said arcuate portion; said arcuate portion has a notch formed on it, opening into the arcuate edge formed by this arcuate portion, and forming a tip oriented toward the upstream side of the counter-knife.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/IB2015/051058, filed Feb. 12, 2015, now pending, which claimsforeign priority to French Patent Application No. FR 14 51178, filedFeb. 14, 2014, the disclosure of which are herein wholly incorporated byreference.

The present invention relates to a machine for treating infectiouswaste, in particular medical waste.

BACKGROUND OF THE INVENTION

The law requires that infectious waste, in particular medical waste, beshredded such that it is not recognizable or reusable, and above allsuch that it can be highly sterilized. To that end, it is known to use ashredding and sterilizing machine for such waste, comprising an upperhopper for receiving waste, a median shredding compartment, and a lowertub for receiving, sterilizing and discharging shredded waste.

The median shredding compartment includes a shredder formed from aparallel series of contrarotating knives, the knives in one seriesalternating with counter-knives. The knives in one series cooperate withthe counter-knives in another, adjacent series, and vice versa.

The existing machines of this type are globally satisfactory, but maynevertheless still be perfected.

Indeed, a drawback of such a machine is the fact that shreddingefficiency of this machine is not perfect. The result is frequently thatfragments of waste remain too large in consideration of what isrequired. A calibration grid or similar means must therefore be providedbetween the shredding chamber and the lower chamber, which has atendency to clog when waste is wet, making the shredder inoperative.

OBJECTS OF THE INVENTION

The invention's main objective is to overcome this major disadvantage.

The Utility Model application No. DE 93 12 163 U1 discloses a wasteshredder for shredding waste such as cans, tires, plastic containers,oil filters, including two sets of contrarotating knives and includinginserts forming counter-knifes. In the version of this shredder shown inFIG. 5 of this document, it is indicated that the counter-knifes includeprojections arranged at the cutting plates. These projections formarcuate portions near which passes the teeth of the knives; eachprojection has a limited length, is situated downstream of the planepassing by the axes of the series of knives and counter-knife, and ispreceded by a portion of counter-knife located remotely from the teethof the corresponding knife, so that there exists, between the projectionand said portion of the counter-knife, a slight and shallow step, havinga very opened “V” shape.

The machine described in this prior document is considered as notsuitable for required shredding of medical waste, and as being unable toovercome the aforementioned drawback.

SUMMARY OF THE INVENTION

The machine concerned by the invention comprises a waste chargingreceptacle and a shredding assembly for shredding said waste, includinga shredder, this shredder being formed by at least two parallel seriesof contrarotating knives, the knives of one series alternating withcounter-knives of that same series, and the knives of a first seriescooperating with the counter-knives of another adjacent series, and viceversa; the knives are carried by shafts for driving these knives torotate, and the counter-knifes of one series are engaged around theseshafts; the edge of each counter-knife facing the opposite knifeassociated thereto comprises an arcuate portion located on thedownstream side of the shredder relative to the direction of passage ofwaste material between the series of knives and counter-knives, and saidopposite knife comprises teeth that pass in the immediate vicinity ofthat arcuate portion;

-   -   at least one counter-knife of one series has a portion extending        above the axis of the shaft of the same series, so that this        counter-knife forms a closed bearing traversed by this shaft,        this portion of the counter-knife forming an arcuate edge        centered on the axis of another shaft of the shredder, this        arcuate edge completing said arcuate portion and making the        arcuate edges of said portions extend not only below the plane        defined by the axis of the shafts but also above this plan;    -   said arcuate portion has a notch formed on it, opening into the        arcuate edge formed by this portion, and forming a tip oriented        toward the upstream side of the counter-knife.

It will be understood by “in the immediate vicinity”, it is defined avery short distance, corresponding to the sufficient clearance for thepassage of the teeth of the corresponding knife, i.e. about a millimeterat most.

All the characteristics above makes it possible to constitute anextended area of passage of the teeth of the opposite knife near thearcuate edges of the counter-knife, and said tip formed by said notchconstitutes a catching zone for a fragment of waste present between theknife and the counter-knife. This tip makes it possible to retain thisfragment until passage of the consecutive tooth of the knife facing saidtip, which makes it possible to perform additional shearing or shreddingof that fragment.

When the set of counter-knives comprised by the shredder has such anotch, and therefore such a tip, the shredder not only comprises a firstshearing zone at the teeth of the knives and a second shearing zonebetween the edges of the teeth of the knives and the upper edges of thecounter-knives, but also a third shearing zone between said tips andsaid consecutive teeth of the knives as well as a fourth active zone,made up of the alternating arrangement of said tips of one counter-knifeand of one adjacent counter-knife. These tips make up calibration zonesin the form of a sort of comb, which allow the shredded waste to bedriven again into the aforementioned shearing zones if this waste hasdimensions larger than the dimensions of the passage zone initiallydefined.

The effectiveness of the obtained shredding is thus greatly improved andmakes it possible to eliminate any need for calibration downstream fromthe shredder.

Preferably, the edges of said arcuate portion and of said portion of thecounter-knife jointly form a circular arcuate zone extending over an arcof approximately thirty degrees, preferably of thirty degrees.

Preferably, said notch is delimited on its side closest to the axis ofthe shaft crossing said counter-knife, by a straight edge of thecounter-knife, directed perpendicularly to the plane defined by the axesof said shafts, and, on its side opposite from this axis, by an obliqueedge.

This notch shape is particularly efficient.

Preferably, said straight edge and said oblique edge are rectilinear andform between them an angle of about forty degrees, preferably of fortydegrees.

According to another aspect of the invention,

-   -   the receptacle for loading waste has a constant cross-section        between a waste loading opening and a communication opening with        the shredder; and    -   the machine comprises a pushing means making it possible to push        the waste toward the shredder, this pushing means being a plate        translatable in the waste loading receptacle, parallel to the        axis along which this receptacle has said constant        cross-section, this plate having dimensions such that only an        interstice exists between the edge wall of the plate and the        walls defining said waste loading receptacle; the plate is        movable between a withdrawn position, in which it is able to be        freed from said waste loading opening, and an end-of-travel        position, in which it is situated near said communication        opening.

The plate makes it possible, through its movement, to push all of thewaste toward the shredding compartment, without requiring repeatedactuation by an operator as with a shaft according to the prior art. Theinterstice formed by this plate with the walls of the receptacleeliminates the risk of waste, or fragments of waste, rising up theshredder, passing above it. In said end-of-travel position, there is nolonger a risk of fragments of shredded waste becoming jammed between theplate and the walls of the receptacle, and the machine does not compriseany hollow seat in which such fragments may accumulate.

Furthermore, the seal makes it possible to temporarily separate thereceptacle and the shredding compartment, to disinfect and sterilize theshredding compartment under conditions not required for said receptacle.The assembly makes it possible for the waste loading receptacle to bedisinfected and sterilized by the same disinfection and sterilizationmeans as those disinfecting and sterilizing the shredding compartmentand, when the machine comprises one, the lower receiving tub,sterilizing and discharging the shredded waste.

Preferably, the machine comprises a sealing gasket movable between aretracted position, in which this sealing gasket does not hinder themobility of the plate in the waste loading receptacle, and a sealingposition, in which the sealing gasket produces, in said end-of-travelposition of the plate, sealing between the plate and the walls of saidreceptacle.

The risk of fragments of waste rising up in the waste chargingreceptacle is thus eliminated. Furthermore, this sealing gasket is usedto momentarily separate the receptacle and the shredder assembly, forthe production of a disinfection and sterilization of the shredderassembly at conditions not required for said receptacle.

The sealing gasket may in particular be inflatable, such that thepassage of this sealing gasket from said retracted position to saidsealing position is done by inflating this sealing gasket and,conversely, the passage of this sealing gasket from said sealingposition to said retracting position is done by deflating this sealinggasket.

According to one possibility, the sealing gasket is housed in a seatarranged in the walls defining the waste loading receptacle. In saidsealing position, this sealing gasket then presses on the edge wall ofsaid plate, this edge being smooth.

According to another possibility, the sealing gasket is housed in a seatarranged in the edge wall of said plate and then presses, in saidsealing position, on the walls defining the waste loading receptacle.These walls are then smooth, such that there is no risk of accumulationof waste fragments. The sealing gasket may, in the retracted position,rub slightly against the walls of the receptacle and thus form a meansfor scraping these walls.

The machine may comprise means for blocking the plate in saidend-of-travel position, in particular in the form of at least one latchengaging the plate and at least one of the walls defining said wasteloading receptacle.

These blocking means immobilize the plate in this end-of-travel positionand greatly reduce or eliminate the exertion of wearing forces on thesealing gasket.

Preferably, in said withdrawn position, the plate is completely housedin a cover comprised by the machine, this cover being movable between aposition covering said waste loading opening, in which it closes thatopening, and a retracted position, in which it does not hinder theloading of waste in said receptacle.

The plate can thus be completely freed from this opening, which allowseasy loading of the waste.

Preferably, the means for actuating the plate comprise at least twoseries of crossed-bars pivotally connected to one another, on twoopposite sides of the plate.

Such crossed-bars allow perfect guidance of the plate between itsaforementioned withdrawn and end-of-travel positions.

According to another aspect of the invention,

-   -   the shredder is housed in a moving drawer sliding inside a        receiving compartment comprised by the structure of the machine,        this receiving compartment being defined by side walls and a        rear wall, which comprises an opening;    -   the drawer has a distal boss able, in the fully engaged position        of this drawer in said receiving compartment, to be engaged in        an adjusted manner in said opening comprised by said rear wall;    -   the machine comprises a cap able to envelop the part of the        distal boss that protrudes past said rear wall in the fully        engaged position of the drawer in said receiving compartment,        this cap being provided with a flange intended to be bolted on        said rear wall, this flange having, at its inner edge, a beveled        surface, and    -   the machine comprises a seal able to be engaged in an adjusted        manner around said part of the distal boss that protrudes past        said rear wall in the fully engaged position of the drawer in        said receiving compartment, until it comes into contact with        said rear wall and is pressed by said beveled surface of the cap        when this cap is bolted to said rear wall.

The assembly of the shredder in the machine is thus done by engaging thedrawer that contains the shredder in the shredding compartment, untilsaid distal boss is engaged in an adjusted manner through said openingcomprised by said rear wall. The seal is next placed around this bossuntil it is in contact with this rear wall, then the cap is placed onthe boss and is bolted to this rear wall so as to press the seal.

The invention therefore consists of providing two structures around theshredder, said drawer and said receiving compartment, and providing avery strong distal connection of this drawer to this receivingcompartment, by pressing of said seal over its entire periphery. Thisconnection makes it possible to create sealing between the inside andthe outside of the tub. Furthermore, this connection makes it possibleto produce isostatic mechanical blocking of said two structures, whichmakes it possible, if the geometry of the shredder or the tub is notperfect (which may happen, given that some of these parts are made bymechanized welding), to react the excessive play that would then existbetween the rear part of the shredder and said opening. This sameisostatic mechanical blocking also makes it possible to react aperpendicularity or parallelism flaw between the bearing face againstthe seal and said boss. In other words, when the seal is pressed, itwill not create stresses on the shredder and will simply be placedplastically around said boss comprised by the shredder.

According to still another aspect of the invention,

-   -   the shredder is formed by at least two parallel series of        contrarotating knives, the knives of one series alternating with        the counter-knives of that same series, and the knives of a        first series cooperating with the counter-knives of another        adjacent series, and vice versa, and    -   at least one knife comprises at least one cell emerging in at        least one of its faces turned toward the adjacent counter-knife,        or at least one counter-knife comprises at least one cell        emerging in at least one of its faces turned toward the adjacent        knife, this cell being intended to be filled with lubricating        grease and to thus form a grease reserve.

Thus, when a series of sterilization and disinfection cyclesimplementing a hot fluid, in particular steam, tends to reduce or eveneliminate the quantity of grease present in the interface between aknife and the adjacent counter-knife, the subsequent rotation of theknife relative to the adjacent counter-knife causes a withdrawal ofgrease in that cell due to the viscosity of said grease, and thereforerecharging of that interface with grease. As a result, the interruptionsof the machine to recharge the interfaces of the knives andcounter-knives with grease can be significantly spaced out.

Such a cell may emerge in only one of the faces of a knife or acounter-knife; preferably, however, this cell emerges in both faces of aknife or a counter-knife.

Preferably, a cell is arranged in each counter-knife and emerges in bothfaces of said counter-knife.

The invention will be well understood, and other features and advantagesthereof will appear, in reference to the appended diagrammatic drawing,showing, as a non-limiting example, one preferred embodiment of themachine in question.

BRIEF DESCRIPTION OF THE DRAWINGS

In this drawing,

FIG. 1 is a side view of this machine, in longitudinal cross-section, apressing plate comprised by this machine being in a withdrawn position;

FIG. 2 is a view of the machine similar to FIG. 1, said pressing platebeing in a lowering end-of-travel position;

FIG. 3 is a very enlarged view of the machine situated at thisend-of-travel position, said pressing plate not being in this sameposition;

FIG. 4 is a view similar to FIG. 3, said pressing plate being in saidend-of-travel position;

FIG. 5 is a perspective view of a shredding assembly and a lower tub forreceiving shredded waste, comprised by the machine;

FIG. 6 is an enlarged cross-sectional view of this shredding assembly;

FIG. 7 is an exploded view of various members making up the shreddercomprised by the machine;

FIG. 8 is a view of the shredding compartment similar to FIG. 6, inlongitudinal section passing through one of the shafts comprised by theshredder;

FIG. 9 is a sectional front view of a knife and a counter-knifecomprised by the shredder;

FIG. 10 is a side view of this machine, in longitudinal section,according to one alternative embodiment of a sealing gasket comprised bysaid pressing plate, and

FIG. 11 is an enlarged view of a detail appearing in this FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show a machine 1 for treating infectious waste, inparticular medical waste, essentially comprising a waste loadingreceptacle 2, a shredding assembly 3 for shredding this waste and alower tub 4 for receiving, sterilizing and discharging the shreddedwaste. The other elements visible in these figures (electrical cabinet,steam generating unit, etc.) are well known in themselves and are notpart of the invention; they will therefore not be described morespecifically.

The receptacle 2 has a constant cross-section between an upper wasteloading opening and a lower communication opening with a shreddingcompartment, including a shredder 5, comprised by the shredding assembly3.

In the version of the machine shown in FIGS. 1 to 4, the receptacle 2comprises, slightly withdrawn from this lower opening, a hollow seat 6(see FIGS. 3 and 4) in which an inflatable seal 7 is placed. This seal 7defines a closed inner chamber that is connected to a pressurized fluidsource (not shown). Supplying this chamber with this fluid makes itpossible to expand the seal 7, causing it to go from a retractedposition, shown in FIG. 3, in which this seal does not protrude from theseat 6, to a sealing position, shown in FIG. 4, in which this sealprotrudes from the seat 6 and is pressed against the edge walls of apressing plate 10, described later, thus producing sealing between thisplate 10 and the walls of this receptacle 2.

In the alternative embodiment of the machine 1 shown in FIG. 10, theseat 6, containing the seal 7, is arranged in the edge walls of theplate 10 and the portions of the walls of the receptacle 2 situatedslightly withdrawn from said lower opening are smooth and in thecontinuation of the rest of the walls of the receptacle 2.

In association with the receptacle 2, the machine comprises a pressingassembly for the waste in this receptacle, and an upper sliding cover11.

The waste pressing assembly comprises said pressing plate 10, two seriesof pivotally-linked cross bars 12 and structures 13 connecting theseseries of cross bars 12 to the plate 10 on the one hand, and to thecover 11 on the other hand.

As shown in FIGS. 1, 2 and 10, the pressing plate 10 has dimensions suchthat only an interstice exists between its edge walls and the wallsdefining the receptacle 2. This plate 10 is translatable in thereceptacle 2, through the unfolding/folding of the crossed-bars 12,parallel to the axis along which this receptacle 2 has said constantcross-section. This mobility occurs between an upper withdrawn position,shown in FIG. 1, in which it is completely retracted in the cover 11,and a lower end-of-travel position, shown in FIG. 2, in which it issituated near said communication opening, and in which the seal 7 isable to perform the aforementioned sealing.

The cover 11 is inwardly hollow, so as to house the plate 10, the seriesof crossed-bars 12, said connecting structures 13 and a jack foractuating the crossed-bars 12. It is movable by sliding between theillustrated position completely covering the waste loading opening, inwhich it closes that opening tightly, and a lateral withdrawn position,in which it completely frees said opening and therefore does not hinderthe loading of waste in the receptacle 2.

Said connecting structures 13 are formed from frames made of cornerprofiles; the walls on which the branches of the respective crossed-bars12 are mounted comprise apertures making it possible for the pivot pointof one branch of the corresponding crossed-bar 12 to come closer to andfurther from the pivot point of the other branch of that samecrossed-bar.

The machine 1 also comprises latches 14 mounted on two opposite walls ofthe receptacle 2, both of which are, in said lower end-of-travelposition, received in corresponding strikes arranged in the framesforming said connecting structures 13.

In reference to FIGS. 5 to 8, it appears that the waste shreddingassembly 3 essentially comprises the shredder 5, formed from twoparallel shafts 15 each including a series of knives 16 and alternatingcounter-knives 17, a shredding compartment 18 housing this shredder 5,and an actuating assembly for actuating these shafts 15 in acontrarotating manner.

The knives 16 in one series cooperate with the counter-knives 17 in theother series, and vice versa, as particularly shown in FIG. 9.

In reference to this FIG. 9, it appears that the shafts 15 have ahexagonal section and that each knife 16 has a central opening formed bythe superposition of two hexagonal apertures, offset from one another by30°, the dimensions of these apertures being such that they allow theadjusted engagement, and wedging, of the knives 16 on the shafts 15. Asparticularly shown in FIG. 8, the successive knives 16 of a same seriesare offset by 30 degrees, from one knife to an adjacent knife in thesame series.

Each knife 16 has five protruding teeth, forming cutting edges.

Each counter-knife 17 is engaged on the corresponding shaft 15 andcomprises a circular opening in which a sliding ring 20 with a hexagonalopening and circular periphery is housed, this sliding ring 20 beingmounted on the shaft 15. The counter-knife 17 is thus not movable in thecompartment 18 when the corresponding shaft 15 is rotated.

On the side opposite the counter-knife 17 relative to the knife 16, theshredder 5 has an additional counter-knife 19.

The counter-knife 17 has an arc of circle edge turned toward theassociated knife 16, along which the teeth travel comprised by thatknife 16, and has a notch 21 arranged in it, emerging in this same arcof circle edge, and situated on the downstream side of the shredder 5relative to the passage direction of the waste between the series ofknives 16 and counter-knives 17. This notch 21 thus forms a tip 22oriented on the upstream side of the counter-knife 17.

The counter-knife 17 also comprises a cell 23 emerging in both faces ofthe counter-knife 17 turned toward the knives 16 that are adjacent tosaid counter-knife 17 in the same series of knives and counter-knives.This cell 23 is filled with lubricating grease and thus forms a greasereserve, as explained later.

The counter-knife 19 also has an arc of circle edge turned toward theassociated knife 16, along which the teeth travel comprised by thatknife 16. It is fastened on a wall 25 laterally defining the shreddingcompartment 18.

In reference to FIGS. 5 to 8, it appears that this compartment 18 isdefined by a forward wall 24, two side walls 25 and a rear wall 26including a distal boss 27. In the assembled state, the assembly forms adrawer that is placed in a receiving compartment 28 having dimensionsadjusted to those of the drawer, the walls defining this receivingcompartment 28 forming a body with the tub 4. This receiving compartment28 is in particular defined by a rear wall 29 that comprises an openingable to receive the boss 27 in an adjusted manner in the fully engagedposition of the drawer, and also comprises a series of threaded rodsfastened to it around this opening.

The machine 1 also comprises a cap 30 and a seal 31.

The cap 30 is dimensioned to envelop the boss 27 in an adjusted mannerand is provided with a flange intended to be engaged on the threadedrods secured to the wall 29 and to be bolted to the latter. As shown inFIG. 11 in particular, this flange has, at its inner edge, a beveledsurface 32.

The seal 31 is in the form of a ring and is dimensioned to be engaged inan adjusted manner around the boss 27 until it comes into contact withsaid rear wall 29. When the cap 30 is bolted to the latter, said beveledsurface 32 presses this seal 31 over its entire periphery, as shown moreparticularly in FIG. 11.

The actuating assembly of the shredder 5 includes a motor 35 acting onone of the shafts 15, and two pinions 36, wedged on the shafts 15 andmeshing with one another such that the driving of one shaft 15 generatedby the motor 35 is transmitted to the other shaft 15.

The tub 4 has a longitudinal opening 40 through which the shredded wastecan be removed from it. This opening 40 is closed by a sliding cover 41,movable between a tight closing position of this opening and a withdrawnposition, in which this cover 41 completely frees that opening.

As will be understood, the plate 10 makes it possible, through itsmovement, to push all of the waste toward the shredding compartment 18,without requiring repeated actuation by an operator as with a shaftaccording to the prior art. The interstice formed by this plate 10 withthe walls of the receptacle 2 eliminates, jointly with the sealing madepossible by the seal 7, any risk of waste, or fragments of waste, risingup the shredder 5 and passing above this plate 10, or of such waste orfragments accumulating in a hollow seat. The crossed-bars 12 allowperfect guidance of the plate 10 between its withdrawn and end-of-travelpositions, preventing any risk of jamming of this plate in thisreceptacle.

The plate 10 and the seal 7 further make it possible to temporarilyseparate the receptacle and the shredding compartment 18, to disinfectand sterilize the shredding compartment under conditions not requiredfor the receptacle 2. The latches 14 immobilize the plate 10 in thisend-of-travel position, which protects the seal 7 from the wearingforces generated by this disinfection and sterilization.

The assembly of the shredder 5 in the machine 1 is done by engaging thedrawer that contains the shredder in the receiving compartment 28, untilthe boss 27 is engaged through the passage opening arranged in the rearwall 29. The seal 31 is next placed around this boss 27 until it is incontact with this rear wall 29, then the cap 30 is placed in an adjustedmanner on the boss 27 and is bolted to this rear wall 29 so as to pressthe seal 31 via the beveled wall 32.

Two structures are thus provided around the shredder 5, said drawer 25and said receiving compartment 28, and the pressing of the seal 31 overits entire periphery, by the cap 30, makes it possible to produce a verystrong and isostatic distal connection of this drawer to this receivingcompartment. This connection is perfectly able to withstand repeatedforces experienced by the shredder 5, while allowing easy disassembly ofthe shredder, by simple disassembly of the cap 30 and removal of theseal 31 from around the boss 27.

Each cell 23 allows a recharge of the interface between a counter-knife17 and the two adjacent knives 16 when a series of sterilization anddisinfection cycles implementing steam tends to reduce or even eliminatethe quantity of grease present in these interfaces. As a result, theinterruptions in the use of the machine 1 to recharge the interfaces ofthe knives 16 and counter-knives 17 with grease can be significantlyspaced out.

Furthermore, the tip 22 constitutes a catching zone for a fragment ofwaste present between a knife 16 and a counter-knife 17 and makes itpossible to retain that fragment until passage of the consecutive toothof the knife 16 across from that tip 22, which makes it possible toperform shearing or additional shredding of that fragment. Theeffectiveness of the obtained shredding is greatly improved and makes itpossible to eliminate any need for sieving downstream from the shredder5.

As appears from the preceding, the invention provides a machine 1 havingthe aforementioned decisive advantages relative to the similar machinesof the prior art.

Of course, the invention is not limited to the embodiment describedabove as an example, but encompasses all embodiments covered by theappended claims.

What is claimed is:
 1. A machine for treating waste, comprising: areceptacle for loading waste; and a shredding assembly for shreddingsaid waste, including a shredder, this shredder being formed by at leasttwo parallel series of contrarotating knives, the knives of one seriesalternating with counter-knives of that same series, and the knives of afirst series cooperating with the counter-knives of another adjacentseries, and vice versa; the knives are carried by shafts for drivingthese knives to rotate, and the counter-knifes of one series are engagedaround these shafts; the edge of each counter-knife facing the oppositeknife associated thereto comprises an arcuate portion located on thedownstream side of the shredder relative to the direction of passage ofwaste material between the series of knives and counter-knives, and saidopposite knife comprises teeth that pass in the immediate vicinity ofthat arcuate portion; at least one counter-knife of one series has aportion extending above the axis of the shaft of the same series, sothat this counter-knife forms a closed bearing traversed by this shaft,this portion of the counter-knife forming an arcuate edge centered onthe axis of another shaft of the shredder, this arcuate edge completingsaid arcuate portion and making the arcuate edges of said portionsextend not only below the plane defined by the axis of the shafts butalso above this plan; said arcuate portion has a notch formed on it,opening into the arcuate edge formed by this arcuate portion, andforming a tip oriented toward the upstream side of the counter-knife. 2.The machine according to claim 1, wherein all the counter-knivescomprised by the shredder has such a notch, and therefore such a tip. 3.The machine according to claim 1, wherein the edges of said arcuateportion and of said portion of the counter-knife jointly form a circulararcuate zone extending over an arc of approximately thirty degrees 4.The machine according to claim 1, wherein said notch is delimited on itsside closest to the axis of the shaft crossing said counter-knife, by astraight edge of the counter-knife, directed perpendicularly to theplane defined by the axes of said shafts, and, on its side opposite fromthis axis, by an oblique edge.
 5. The machine according to claim 4,wherein said straight edge and said oblique edge are rectilinear andform between them an angle of about forty degrees.
 6. The machineaccording to claim 1, wherein the waste is infectious medical waste.